Ultracold atomic gases and neutron matter are fermionic systems which exhibit pairing gaps that are comparable to the Fermi energy and are thus the largest ever encountered in nature or the laboratory. In this work we use microscopic simulation methods to attack both these systems.
We first give some background material on the experimental situation in cold-atom physics, along with some basic facts about neutron-star structure. We then move to a discussion of the many-body problem in its simplest form: the two-body problem in scattering theory, allowing us to introduce a useful phenomenological potential, along with some details on the atom-atom and neutron-neutron interactions. The many-body problem is then attacked at the mean-field BCS theory level. These BCS calculations are performed both in the thermodynamic limit and for finite particle numbers, laying the groundwork for our microscopic Quantum Monte Carlo simulation methods, which are described in due course with a strong emphasis on the BCS-like trial wave function we have utilized.
We then go on to provide our main results, starting with unpolarized cold atomic gases in the BCS regime and at unitarity. We calculate the zero-temperature equation of state, the pairing gap, the quasiparticle excitation spectrum, the momentum distribution, and the pair-distribution functions in an attempt to elucidate the strongly paired character of this system, and directly compare our predictions with experiment. An intriguing variation is then discussed, by considering pairing between atoms with different masses; we separately discuss the unpolarized case, then examine the phase stability by showing calculations for the polarized case, and conclude this part by analyzing the consequences of our results for the experimentally relevant harmonically trapped case.
Results for the aforementioned observables are also given for the case of low-density neutron matter, which is characterized by a finite effective range and a more complicated interaction. These results are also compared with our cold-atom predictions and also with other many-body approaches to neutron matter, in the hope that the atomic physics predictions can help to constrain nuclear theory.
|School:||University of Illinois at Urbana-Champaign|
|School Location:||United States -- Illinois|
|Source:||DAI-B 71/01, Dissertation Abstracts International|
|Subjects:||Low Temperature Physics, Atomic physics, Nuclear physics|
|Keywords:||Cold atoms, Neutron stars, Paired fermions, Superfluidity|
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